1. Field of the Invention
This invention relates to a method of joining silicon nitride having a thin layer of active silicon metal to carbon steel, wherein the active silicon layer is formed through the thermal dissociation of silicon nitride (Si.sub.3 N.sub.4) into silicon (Si) and nitrogen gas (N.sub.2). The active silicon layer may be directly joined to carbon steel via an induced eutectic melting reaction between Si and the iron (Fe) found in carbon steel, or via brazing of two materials such as Ag--Cu alloys.
2. Description of the Related Art
Recently, ceramic-based materials have been applied to commercial machine parts in an effort to improve efficiency and performance. The fabrication of such ceramics containing parts has generally been carried out by joining ceramic and metal, such as by joining Si.sub.3 N.sub.4 and carbon steel. Due to intrinsic properties associated with different materials, however, the techniques designed to join such materials remain difficult. For example, the interfacial energy between silicon nitride and Ag--Cu alloys (Y.sub.Si3N4/AgCu) is larger than the sum of the surface energy of silicon nitride (Y.sub.S3N4) and Ag--Cu alloys (Y.sub.Ag--Cu) alone. Therefore, these two materials do not completely wet on contact, and the joining of these two materials is difficult.
To overcome the above-described problems, Ag--Cu--Ti alloys containing silicon nitride and a highly active metal (e.g., Ti) have been used instead of Ag--Cu alloys. However, the Ag--Cu--Ti system is very expensive (about ten times higher than Ag--Cu alloys), which result in higher production costs.
Therefore, other methods have been used to join silicon nitride to carbon steel in which only the surface of silicon nitride is coated with a highly active metals (e.g., Ti, Zr) via physical method such as sputtering. This type of method activates the surface of silicon nitride such that joining can be made using Ag--Cu alloys. However, this joining method has the disadvantages of not only being very complicated but of requiring a large initial investment for sputtering equipment, which also results in increased production costs. Therefore, there is a need for a simple and economical process to join silicon nitride and carbon steel.